1. Field of the Invention
The present invention relates to a bar code scanner which optically reads a bar code.
2. Description of the Related Art
One type of bar code scanner has heretofore been known which has a light-emitting element, a light-receiving element, an optical means adapted to apply a light beam from the light-emitting element to a bar code area and to lead the light reflected from the bar code area to the light-receiving element, and an electrical processing circuit.
In this type of bar code scanner, an extremely important factor in determining the resolution of its optical system is a mechanism for retaining the distal end portion of the sensor at which a lens which is a constituent element of the optical means is exposed to the outside. One example of the retaining mechanism will be explained below with reference to FIG. 3 which is a fragmentary sectional view thereof.
In FIG. 3, the reference numeral 1 denotes a sensor body which supports a light-emitting element, a light-receiving element and an optical means, (not shown), together with a lens 2 and the like. A split casing 3 which consists of a pair of upper and lower split casing members houses the sensor body 1 in such a manner that a clearance X is defined therebetween so as to allow the sensor body 1 to move along the longitudinal axis thereof, that is, in the horizontal direction as viewed in FIG. 3, and the distal end of the sensor body 1 projects from one end of the casing 3. An intermediate cap 4 is adapted for joining the respective ends of the upper and lower casing members of the split casing 3 and thereby connecting them together. The cap 4 has a retaining projection 6 formed on the inner periphery thereof which is fitted into an engaging recess 5 formed in the outer periphery of each of the portions 3a which extend from the distal end of the split casing 3. A distal end cap 7 has a through-hole 7a for exposing a light incident and emergent portion of the sensor body 1, that is, the lens 2, to the outside. The distal end cap 7 is detachably threaded to the intermediate cap 4.
In the above-described conventional device, the distance l between the front face of the lens 2 and the open end of the through-hole 7a must be set with a high degree of accuracy since it is an important factor in determining the resolution of the optical system of the sensor body 1. However, cumulation of possible dimensional errors in relation to the split casing 3, the intermediate cap 4 and the distal end cap 7 may hinder the distance l from being set with the required dimensional accuracy at all times. For this reason, the sensor body 1 is adapted to be movable relative to the split casing 3 along the longitudinal axis, that is, in the horizontal direction as viewed in FIG. 3, thereby allowing dimensional adjustment.
The above-described conventional device, however, needs to provide the clearance X between the sensor body 1 and the inner periphery of the split casing 3 in order to allow the longitudinal movement of the sensor body 1, and this clearance X also leads to the following disadvantage. When the retaining portion 6 of the intermediate cap 4 is fitted into the engaging portion 5 formed on each extending portion 3a of the split casing 3, the clearance X allows the portion 3a to be pressed excessively and thereby bent inwardly, and the deformation of the portion 3a may continue while leaving the fitting between the engaging portion 5 and the retaining portion 6 in an incomplete state.